Dental compositions containing nanofillers and related methods

ABSTRACT

The present invention features ionomer compositions containing nanofillers. The compositions can be used in a variety of dental and orthodontic applications, for example, as adhesives, cements, restoratives, coatings and sealants.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/847,781,filed May 17, 2004, now issued as U.S. Pat. No. 7,156,911, thedisclosure of which is incorporated by reference in its entirely herein.

FIELD OF THE INVENTION

The present invention relates to hardenable dental and orthodonticcompositions filled with nanosized particles. More specifically, theinvention relates to ionomer and resin modified ionomer compositionscontaining nanofillers. The compositions can be used in a variety ofapplications, for example, as adhesives, cements, restoratives,coatings, and sealants.

BACKGROUND

The restoration of decayed dental structures including caries, decayeddentin or decayed enamel, is often accomplished by the sequentialapplication of a dental adhesive and then a dental material (e.g., arestorative material) to the relevant dental structures. Similarcompositions are used in the bonding of orthodontic appliances(generally utilizing an orthodontic adhesive) to a dental structure.Often various pretreatment processes are used to promote the bonding ofadhesives to dentin or enamel. Typically, such pretreatment stepsinclude etching with, for example, inorganic or organic acids, followedby priming to improve the bonding between the tooth structure and theoverlying adhesive.

A variety of dental and orthodontic adhesives, cements, and restorativesare currently available. Compositions including fluoroaluminosilicateglass fillers (also known as glass ionomer or “GI” compositions) areamong the most widely used types of dental materials. These compositionshave a broad range of applications such as filling and restoration ofcarious lesions; cementing of, for example, a crown, an inlay, a bridge,or an orthodontic band; lining of cavity; core construction; and pit andfissure sealing.

There are currently two major classes of glass ionomers. The firstclass, known as conventional glass ionomers, generally contains as mainingredients a homopolymer or copolymer of an α,β-unsaturated carboxylicacid, a fluoroaluminosilicate (“FAS”) glass, water, and optionally achelating agent such as tartaric acid. These conventional glass ionomerstypically are supplied in powder/liquid formulations that are mixed justbefore use. The mixture undergoes self-hardening in the dark due to anionic acid-base reaction between the acidic repeating units of thepolycarboxylic acid and cations leached from the basic glass.

The second major class of glass ionomers is known as hybrid glassionomer or resin-modified glass ionomers (“RMGI”). Like a conventionalglass ionomer, an RMGI employs an FAS glass. An RMGI also contains ahomopolymer or copolymer of an α,β-unsaturated carboxylic acid, an FASglass, and water; however, the organic portion of an RMGI is different.In one type of RMGI, the polyacid is modified to replace or end-cap someof the acidic repeating units with pendent curable groups and aphotoinitiator is added to provide a second cure mechanism. Acrylate ormethacrylate groups are typically employed as the pendant curable group.In another type of RMGI, the composition includes a polycarboxylic acid,an acrylate or methacrylate-functional monomer or polymer, and aphotoinitiator. The polyacid may optionally be modified to replace orend-cap some of the acidic repeating units with pendent curable groups.A redox or other chemical cure system may be used instead of or inaddition to a photoinitiator system. RMGI compositions are usuallyformulated as powder/liquid or paste/paste systems, and contain water asmixed and applied. They may partially or fully harden in the dark due tothe ionic reaction between the acidic repeating units of thepolycarboxylic acid and cations leached from the glass, and commercialRMGI products typically also cure on exposure of the cement to lightfrom a dental curing lamp.

There are many important benefits provided by glass ionomercompositions. For example, fluoride release from glass ionomers tends tobe higher than from other classes of dental compositions such as metaloxide cements, compomer cements, or fluoridated composites, and thusglass ionomers are believed to provide enhanced cariostatic protection.Another advantage of glass ionomer materials is the very good clinicaladhesion of such cements to tooth structure, thus providing highlyretentive restorations. Since conventional glass ionomers do not need anexternal curing initiation mode, they can generally be placed in bulk asa filling material in deep restorations, without requiring layering.

One of the drawbacks of conventional glass ionomers is that thesecompositions are somewhat technique sensitive when mixed by hand. Theyare typically prepared from a powder component and a liquid component,thus requiring weighing and mixing operations prior to application. Theaccuracy of such operations depends in part on operator skill andcompetency. When mixed by hand, the powder component and the liquidcomponent are usually mixed on paper with a spatula. The mixingoperation must be carried out within a short period of time, and askilled technique is needed in order for the material to fully exhibitthe desired characteristics (i.e., the performance of the cement candepend on the mixture ratio and the manner and thoroughness of mixing).Alternatively, some of these inconveniences and technique sensitivitieshave been improved by utilization of powder liquid capsule dispensingsystems that contain the proper proportion of the powder and liquidcomponents. While capsules provide proper proportions of the powder andliquid components, they still require a capsule activation step tocombine the two components followed by mechanical mixing in a dentaltriturator.

Conventional glass ionomers may also be quite brittle as evidenced bytheir relatively low flexural strength. Thus, restorations made fromconventional glass ionomers tend to be more prone to fracture in loadbearing indications. In addition, glass ionomers are often characterizedby high visual opacity (i.e., cloudiness), especially when they comeinto contact with water at the initial stage of hardening, resulting inrelatively poor aesthetics.

Cured RMGIs typically have increased strength properties (e.g., flexuralstrength), are less prone to mechanical fracture than conventional glassionomers, and typically require a primer or conditioner for adequatetooth adhesion.

SUMMARY

The present invention provides stable ionomer compositions containingnanofillers that provide the compositions with improved properties overprevious ionomer compositions. In one embodiment, the present inventionfeatures a hardenable dental composition comprising a polyacid; anacid-reactive filler; at least 10 percent by weight nanofiller or acombination of nanofillers each having an average particle size no morethan 200 nanometers; and water. In another embodiment, the compositionfurther comprises a polymerizable component. Generally, thepolymerizable component is an ethylenically unsaturated compound,optionally with acid functionality.

The polyacid component of the composition typically comprises a polymerhaving a plurality of acidic repeating groups. The polymer may besubstantially free of polymerizable groups, or alternatively it maycomprise a plurality of polymerizable groups. In some implementations,the polyacid and the ethylenically unsaturated compound with acidfunctionally are the same.

The acid-reactive filler is generally selected from metal oxides,glasses, metal salts, and combinations thereof. Typically, theacid-reactive filler comprises an FAS glass. One of the advantages ofthe present invention is that a hardenable composition may be preparedwith less acid-reactive filler than previous GI and RMGI compositions.Accordingly, in one embodiment, the composition of the inventioncomprises less than 50 percent by weight, in some implementations lessthan 30 or less than 20 weight percent, acid-reactive filler, typicallyan FAS glass.

In another embodiment of the invention, the acid-reactive fillercomprises an oxyfluoride material, which is typically nanostructured,e.g., provided in the form of nanoparticles. Generally, theacid-reactive oxyfluoride material is non-fused and includes at leastone trivalent metal (e.g., aluminum, lanthanum, etc.), oxygen, fluorine,and at least one alkaline earth metal (e.g. strontium, calcium, barium,etc.). The oxyfluoride material may be in the form of a coating onparticles or nanoparticles, such as metal oxide particles (e.g.,silica).

In addition to the acid-reactive filler, the composition of theinvention also includes at least one nanofiller, which may be eitheracid reactive or non-acid reactive. Typically, the nanofiller comprisesnanoparticles selected from silica; zirconia; oxides of titanium,aluminum, cerium, tin, yttrium, strontium, barium, lanthanum, zinc,ytterbium, bismuth, iron, and antimony; and combinations thereof. Oftena portion of the surface of the nanofiller is silane treated orotherwise chemically treated to provide one or more desired physicalproperties.

In some embodiments, at least one of the nanofillers and theacid-reactive filler may be the same compound. It may also be desirablefor the nanofiller component to be substantially free of fumed silicaand pyrogenic fillers. In still other embodiments, the nanofiller maycomprise nanoclusters, such as silica clusters, silica-zirconiaclusters, and combinations thereof. The nanoclusters may containreactive ions.

The compositions of the invention may also include one or more optionaladditives, such as, for example, other fillers, pyrogenic fillers,fluoride sources, whitening agents, anticaries agents (e.g., xylitol),remineralizing agents (e.g., calcium phosphate compounds), enzymes,breath fresheners, anesthetics, clotting agents, acid neutralizers,chemotherapeutic agents, immune response modifiers, medicaments,indicators, dyes, pigments, wetting agents, tartaric acid, chelatingagents, surfactants, buffering agents, viscosity modifiers, thixotropes,polyols, antimicrobial agents, anti-inflammatory agents, antifungalagents, stabilizers, agents for treating xerostomia, desensitizers, andcombinations thereof.

The compositions of the invention may further include a photoinitiatorsystem and/or a redox cure system.

Additionally, the compositions may be provided in the form of amulti-part system in which the various components are divided into twoor more separate parts. Typically, the composition is a two-part system,such as a paste-paste composition, a paste-liquid composition, apaste-powder composition, or a powder-liquid composition.

As discussed above, one of the features of the present invention is thatit provides a hardenable ionomer composition while using lessacid-reactive filler than conventional glass ionomers. This facilitatesthe preparation of a two-part, paste-paste composition, which isgenerally desirable because of the ease of mixing and dispensing of sucha system compared to, for example, a powder-liquid system.

Compositions according to the invention are useful in a variety ofdental and orthodontic applications, including dental restoratives,dental adhesives, dental cements, cavity liners, orthodontic adhesives,dental sealants, and dental coatings. The compositions may be used toprepare a dental article by hardening to form, for example, dental millblanks, dental crowns, dental fillings, dental prostheses, andorthodontic devices.

The ionomer compositions of the invention generally exhibit goodaesthetics, low visual opacity (generally no more than about 0.50, insome implementations no more than about 0.40 or 0.30, upon hardening, asdetermined by the Visual Opacity (MacBeth Values) Test Method describedherein), radiopacity, durability, excellent polish, polish retention(generally at least 10 percent, in some implementations at least 20percent or at least 30 percent, as determined by the Polish RetentionTest Method described herein), good wear properties, good physicalproperties including mechanical strengths, e.g., flexural, diametraltensile and compressive strengths, and good adhesive strength to toothstructures. Furthermore, the compositions may also provide adhesion toboth dentin and enamel without the need for primers, etchants, orpreconditioners. In addition, the invention provides for easy mixing andconvenient dispensing options made possible by formulation of apaste-paste composition.

Other features and advantages of the present invention will be apparentfrom the following detailed description thereof, and from the claims.

DEFINITIONS

By “hardenable” is meant that the composition can be cured orsolidified, e.g. by heating, chemical cross-linking, radiation-inducedpolymerization or crosslinking, or the like.

By “filler” is meant a particulate material suitable for use in the oralenvironment. Dental fillers generally have an average particle size ofat most 100 micrometers.

By “nanofiller” is meant a filler having an average primary particlesize of at most 200 nanometers. The nanofiller component may be a singlenanofiller or a combination of nanofillers. Typically the nanofillercomprises non-pyrogenic nanoparticles or nanoclusters.

By “paste” is meant a soft, viscous mass of solids dispersed in aliquid.

By “acid-reactive filler” is meant a filler that chemically reacts inthe presence of an acidic component.

By “oxyfluoride” is meant a material in which atoms of oxygen andfluorine are bonded to the same atom (e.g., aluminum in an aluminumoxyfluoride). Generally, at least 50% of the fluorine atoms are bondedto an atom bearing an oxygen atom in an oxyfluoride material.

By “nanostructured” is meant a material in a form having at least onedimension that is, on average, at most 200 nanometers (e.g., nanosizedparticles). Thus, nanostructured materials refer to materials including,for example, nanoparticles as defined herein below; aggregates ofnanoparticles; materials coated on particles, wherein the coatings havean average thickness of at most 200 nanometers; materials coated onaggregates of particles, wherein the coatings have an average thicknessof at most 200 nanometers; materials infiltrated in porous structureshaving an average pore size of at most 200 nanometers; and combinationsthereof. Porous structures include, for example, porous particles,porous aggregates of particles, porous coatings, and combinationsthereof.

As used herein “nanoparticles” is used synonymously with “nanosizedparticles,” and refers to particles having an average size of at most200 nanometers. As used herein for a spherical particle, “size” refersto the diameter of the particle. As used herein for a non-sphericalparticle, “size” refers to the longest dimension of the particle.

By “nanocluster” is meant an association of nanoparticles drawn togetherby relatively weak intermolecular forces that cause them to clumptogether, i.e. to aggregate. Typically, nanoclusters have an averagesize of at most 10 micrometers.

The term “ethylenically unsaturated compounds with acid functionality”is meant to include monomers, oligomers, and polymers having ethylenicunsaturation and acid and/or acid-precursor functionality.Acid-precursor functionalities include, for example, anhydrides, acidhalides, and pyrophosphates.

By “dental compositions and dental articles” is meant to includeorthodontic compositions (e.g., orthodontic adhesives) and orthodonticdevices (e.g., orthodontic appliances such as retainers, night guards,brackets, buccal tubes, bands, cleats, buttons, lingual retainers, biteopeners, positioners, and the like).

DETAILED DESCRIPTION

The present invention is directed to dental (including orthodontic)compositions, specifically ionomer compositions, e.g., glass ionomercompositions, containing a nanofiller component (i.e., one or morenanofillers). These hardenable compositions further comprise a polyacid,an acid-reactive filler, an optional polymerizable component, and water.The incorporation of one or more nanofillers into the compositionprovides for improved properties, including enhanced aesthetics (e.g.,low visual opacity) and polish retention, as compared to previouslyknown glass ionomer compositions.

Polymerizable Component

As mentioned above, the hardenable dental compositions of the presentinvention optionally include a polymerizable component. Thepolymerizable component can optionally be an ethylenically unsaturatedcompound with or without acid functionality.

The polymerizable component of the present invention can be part of ahardenable resin. These resins are generally thermosetting materialscapable of being hardened to form a polymer network including, forexample, acrylate-functional materials, methacrylate-functionalmaterials, epoxy-functional materials, vinyl-functional materials, andmixtures thereof. Typically, the hardenable resin is made from one ormore matrix-forming oligomer, monomer, polymer, or blend thereof.

In certain embodiments where the dental composition disclosed in thepresent application is a dental composite, polymerizable materialssuitable for use include hardenable organic materials having sufficientstrength, hydrolytic stability, and non-toxicity to render them suitablefor use in the oral environment. Examples of such materials includeacrylates, methacrylates, urethanes, carbamoylisocyanurates, epoxies,and mixtures and derivatives thereof.

One class of preferred hardenable materials includes materials havingpolymerizable components with free radically active functional groups.Examples of such materials include monomers having one or moreethylenically unsaturated groups, oligomers having one or moreethylenically unsaturated groups, polymers having one or moreethylenically unsaturated groups, and combinations thereof.

In the class of hardenable resins having free radically activefunctional groups, suitable polymerizable components for use in theinvention contain at least one ethylenically unsaturated bond, and arecapable of undergoing addition polymerization. Such free radicallyethylenically unsaturated compounds include, for example, mono-, di- orpoly-(meth)acrylates (i.e., acrylates and methacrylates) such as, methyl(meth)acrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, stearyl acrylate, allyl acrylate, glycerol triacrylete,ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, 1,3-propanediol di(meth)acrylate,trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate,1,4-cyclohexanediol diacrylate, pentaerythritol tetra(meth)acrylate,sorbitol hexacrylate, tetrahydrofurfuryl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,ethoxylated bisphenol A di(meth)acrylate, andtrishydroxyethyl-isocyanurate trimethacrylate; (meth)acrylamides (i.e.,acrylamides and methacrylamides) such as (meth)acrylamide, methylenebis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; the bis-(meth)acrylates of polyethylene glycols(preferably of molecular weight 200-500); copolymerizable mixtures ofacrylated monomers such as those in U.S. Pat. No. 4,652,274 (Boettcheret al.); acrylated oligomers such as those of U.S. Pat. No. 4,642,126(Zador et al.); and vinyl compounds such as styrene, diallyl phthalate,divinyl succinate, divinyl adipate and divinyl phthalate. Other suitablefree radically polymerizable compounds include siloxane-functional(meth)acrylates as disclosed, for example, in WO-00/38619 (Guggenbergeret al.), WO-01/92271 (Weinmann et al.), WO-01/07444 (Guggenberger etal.), WO-00/42092 (Guggenberger et al.) and fluoropolymer-functional(meth)acrylates as disclosed, for example, in U.S. Pat. No. 5,076,844(Fock et al.), U.S. Pat. No. 4,356,296 (Griffith et al.), EP-0 373 384(Wagenknecht et al.), EP-0 201 031 (Reiners et al.), and EP-0 201 778(Reiners et al.). Mixtures of two or more free radically polymerizablecompounds can be used if desired.

The polymerizable component may also contain hydroxyl groups and freeradically active functional groups in a single molecule. Examples ofsuch materials include hydroxyalkyl (meth)acrylates, such as2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate;glycerol mono- or di-(meth)acrylate; trimethylolpropane mono- ordi-(meth)acrylate; pentaerythritol mono-, di-, and tri-(meth)acrylate;sorbitol mono-, di-, tri-, tetra-, or penta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are also available from awide variety of commercial sources, such as Sigma-Aldrich, St. Louis,Mo. Mixtures of ethylenically unsaturated compounds can be used ifdesired.

Polymerizable Component With Acid Functionality

When present, the polymerizable component optionally comprises anethylenically unsaturated compound with acid functionality. Preferably,the acid functionality includes an oxyacid (i.e., an oxygen-containingacid) of carbon, sulfur, phosphorous, or boron.

Such compounds include, for example, α,β-unsaturated acidic compoundssuch as glycerol phosphate monomethacrylates, glycerol phosphatedimethacrylates, hydroxyethyl methacrylate phosphates, citric acid di-or tri-methacrylates, poly(meth)acrylated oligomaleic acid,poly(meth)acrylated polymaleic acid, poly(meth)acrylatedpoly(meth)acrylic acid, poly(meth)acrylated polycarboxyl-polyphosphonicacid, poly(meth)acrylated polychlorophosphoric acid, poly(meth)acrylatedpolysulfonic acid, poly(meth)acrylated polyboric acid, and the like, maybe used as components in the hardenable resin system.

Certain of these compounds are obtained, for example, as reactionproducts between isocyanatoalkyl (meth)acrylates and carboxylic acids.Additional compounds of this type having both acid-functional andethylenically unsaturated components are described in U.S. Pat. No.4,872,936 (Engelbrecht) and U.S. Pat. No. 5,130,347 (Mitra). A widevariety of such compounds containing both the ethylenically unsaturatedand acid moieties can be used. Mixtures of such compounds can be used ifdesired.

Additional ethylenically unsaturated compounds with acid functionalityinclude, for example, polymerizable bisphosphonic acids as disclosed forexample, in U.S. Ser. No. 10/729,497; AA:ITA:IEM (copolymer of acrylicacid:itaconic acid with pendent methacrylate made by reacting AA:ITAcopolymer with sufficient 2-isocyanatoethyl methacrylate to convert aportion of the acid groups of the copolymer to pendent methacrylategroups as described, for example, in Example 11 of U.S. Pat. No.5,130,347 (Mitra)); and those recited in U.S. Pat. No. 4,259,075(Yamauchi et al.), U.S. Pat. No. 4,499,251 (Omura et al.), U.S. Pat. No.4,537,940 (Omura et al.), U.S. Pat. No. 4,539,382 (Omura et al.), U.S.Pat. No. 5,530,038 (Yamamoto et al.), U.S. Pat. No. 6,458,868 (Okada etal.), and European Pat. Application Publication Nos. EP 712,622(Tokuyama Corp.) and EP 1,051,961 (Kuraray Co., Ltd.).

When ethylenically unsaturated compounds with acid functionality arepresent, the compositions of the present invention typically include atleast 1% by weight, more typically at least 3% by weight, and mosttypically at least 5% by weight ethylenically unsaturated compounds withacid functionality, based on the total weight of the unfilledcomposition. Typically, compositions of the present invention include atmost 50% by weight, more typically at most 40% by weight, and mosttypically at most 30% by weight ethylenically unsaturated compounds withacid functionality, based on the total weight of the unfilledcomposition.

Partial or complete hardening of the composition may occur through anacid-reactive filler/polyacid reaction (i.e. an acid/base reaction). Incertain embodiments, the composition also contains a photoinitiatorsystem that upon irradiation with actinic radiation initiates thepolymerization (or hardening) of the composition. Suchphotopolymerizable compositions can be free radically polymerizable.

Free Radical Initiation Systems

For free radical polymerization (e.g., hardening), an initiation systemcan be selected from systems that initiate polymerization via radiation,heat, or redox/auto-cure chemical reaction. A class of initiatorscapable of initiating polymerization of free radically active functionalgroups includes free radical-generating photoinitiators, optionallycombined with a photosensitizer or accelerator. Such initiatorstypically can be capable of generating free radicals for additionpolymerization upon exposure to light energy having a wavelength between200 and 800 nm.

Suitable photoinitiators (i.e., photoinitiator systems that include oneor more compounds) for polymerizing free radically photopolymerizablecompositions include binary and ternary systems. Typical ternaryphotoinitiators include an iodonium salt, a photosensitizer, and anelectron donor compound as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). Preferred iodonium salts are the diaryl iodoniumsalts, e.g., diphenyliodonium chloride, diphenyliodoniumhexafluorophosphate, diphenyliodonium tetrafluoroborate, andtolylcumyliodonium tetrakis(pentafluorophenyl) borate. Preferredphotosensitizers are monoketones and diketones that absorb some lightwithin a range of about 400 nm to 520 nm (preferably, 450 nm to 500 nm).More preferred compounds are alpha diketones that have some lightabsorption within a range of 400 nm to 520 nm (even more preferably, 450to 500 nm). Preferred compounds are camphorquinone, benzil, furil,3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone,1-phenyl-1,2-propanedione and other 1-aryl-2-alkyl-1,2-ethanediones, andcyclic alpha diketones. Most preferred is camphorquinone. Preferredelectron donor compounds include substituted amines, e.g., ethyldimethylaminobenzoate. Other suitable ternary photoinitiator systemsuseful for photopolymerizing cationically polymerizable resins aredescribed, for example, in U.S. Pat. Publication No. 2003/0166737, nowU.S. Pat. No. 6,765,036 (Dede et al.).

Other suitable photoinitiators for polymerizing free radicallyphotopolymerizable compositions include the class of phosphine oxidesthat typically have a functional wavelength range of 380 nm to 1200 nm.Preferred phosphine oxide free radical initiators with a functionalwavelength range of 380 nm to 450 nm are acyl and bisacyl phosphineoxides such as those described in U.S. Pat. No. 4,298,738 (Lechtken etal.), U.S. Pat. No. 4,324,744 (Lechtken et al.), U.S. Pat. No. 4,385,109(Lechtken et al.), U.S. Pat. No. 4,710,523 (Lechtken et al.), and U.S.Pat. No. 4,737,593 (Ellrich et al.), U.S. Pat. No. 6,251,963 (Kohler etal.); and EP Application No. 0 173 567 A2 (Ying).

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges of greaterthan 380 nm to 450 nm include, for example,bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide available under thetrade designation IRGACURE 819 from Ciba Specialty Chemicals, Tarrytown,N.Y.; bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxideavailable under the trade designation CGI 403 from Ciba SpecialtyChemicals; a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one available under the tradedesignation IRGACURE 1700 from Ciba Specialty Chemicals; a 1:1 mixture,by weight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one available under the tradedesignation DAROCUR 4265 from Ciba Specialty Chemicals; and ethyl2,4,6-trimethylbenzylphenyl phosphinate available under the tradedesignation LUCIRIN LR8893X from BASF Corp., Charlotte, N.C.

Typically, the phosphine oxide initiator is present in thephotopolymerizable composition in catalytically effective amounts, suchas from 0.1% by weight to 5% by weight, based on the total weight of thecomposition.

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines useful in theinvention include ethyl 4-(N,N-dimethylamino)benzoate andN,N-dimethylaminoethyl methacrylate. When present, the amine reducingagent is present in the photopolymerizable composition in an amount from0.1% by weight to 5% by weight, based on the total weight of thecomposition. Useful amounts of other initiators are well known to thoseof skill in the art.

Another free-radical initiator system that can alternatively be used inthe dental materials of the invention includes the class of ionicdye-counterion complex initiators including a borate anion and acomplementary cationic dye. Borate salt photoinitiators are described,for example, in U.S. Pat. No. 4,772,530 (Gottschalk et al.), U.S. Pat.No. 4,954,414 (Adair et al.), U.S. Pat. No. 4,874,450 (Gottschalk), U.S.Pat. No. 5,055,372 (Shanklin et al.), and U.S. Pat. No. 5,057,393(Shanklin et al.).

The hardenable resins of the present invention can include redox curesystems that include a polymerizable component (e.g., an ethylenicallyunsaturated polymerizable component) and redox agents that include anoxidizing agent and a reducing agent. Suitable polymerizable componentsand redox agents that are useful in the present invention are describedin U.S. Pat. Publication No. 2003/0166740, (Mitra et al.) and U.S. Pat.Publication No. 2003/0195273, now U.S. Pat. No. 6,982,288 (Mitra etal.).

The reducing and oxidizing agents should react with or otherwisecooperate with one another to produce free-radicals capable ofinitiating polymerization of the resin system (e.g., the ethylenicallyunsaturated component). This type of cure is a dark reaction, that is,it is not dependent on the presence of light and can proceed in theabsence of light. The reducing and oxidizing agents are preferablysufficiently shelf-stable and free of undesirable colorization to permittheir storage and use under typical dental conditions. They should besufficiently miscible with the resin system (and preferablywater-soluble) to permit ready dissolution in (and discourage separationfrom) the other components of the polymerizable composition.

Useful reducing agents include, for example, ascorbic acid, ascorbicacid derivatives, and metal complexed ascorbic acid compounds asdescribed in U.S. Pat. No. 5,501,727 (Wang et al.); amines, especiallytertiary amines, such as 4-tert-butyl dimethylaniline; aromatic sulfinicsalts, such as p-toluenesulfinic salts and benzenesulfinic salts;thioureas, such as 1-ethyl-2-thiourea, tetraethyl thiourea, tetramethylthiourea, 1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixturesthereof. Other secondary reducing agents may include cobalt (II)chloride, ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine(depending on the choice of oxidizing agent), salts of a dithionite orsulfite anion, and combinations thereof. Preferably, the reducing agentis an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include, for example, persulfuric acid and salts thereof, suchas sodium, potassium, ammonium, cesium, and alkyl ammonium salts.Additional oxidizing agents include, for example, peroxides such asbenzoyl peroxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and combinations thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure. In some embodimentsit may be preferred to include a secondary ionic salt to enhance thestability of the hardenable composition as described, for example, inU.S. Pat. Publication No. 2003/0195273, now U.S. Pat. No. 6,982,288(Mitra et al.).

The reducing and oxidizing agents are present in amounts sufficient topermit an adequate free-radical reaction rate. This can be evaluated bycombining all of the ingredients of the hardenable composition exceptfor the filler, and observing whether or not a hardened mass isobtained.

Preferably, the reducing agent is present in an amount of at least 0.01%by weight, and more preferably at least 0.10% by weight, based on thetotal weight (including water) of the components of the hardenablecomposition. Preferably, the reducing agent is present in an amount ofno greater than 10% by weight, and more preferably no greater than 5% byweight, based on the total weight (including water) of the components ofthe polymerizable composition.

Preferably, the oxidizing agent is present in an amount of at least0.01% by weight, and more preferably at least 0.10% by weight, based onthe total weight (including water) of the components of thepolymerizable composition. Preferably, the oxidizing agent is present inan amount of no greater than 10% by weight, and more preferably nogreater than 5% by weight, based on the total weight (including water)of the components of the hardenable composition.

The reducing or oxidizing agents can be microencapsulated as described,for example, in U.S. Pat. No. 5,154,762 (Mitra et al.). This willgenerally enhance shelf stability of the polymerizable composition, andif necessary permit packaging the reducing and oxidizing agentstogether. For example, through appropriate selection of an encapsulant,the oxidizing and reducing agents can be combined with anacid-functional component and optional filler and kept in astorage-stable state. Likewise, through appropriate selection of awater-insoluble encapsulant, the reducing and oxidizing agents can becombined with an FAS glass and water and maintained in a storage-stablestate.

In a further alternative, heat may be used to initiate the hardening, orpolymerization, of free radically active groups. Examples of heatsources suitable for the dental materials of the invention includeinductive, convective, and radiant. Thermal sources should be capable ofgenerating temperatures of at least 40° C. and at most 150° C. undernormal conditions or at elevated pressure. This procedure is preferredfor initiating polymerization of materials occurring outside of the oralenvironment.

Yet another alternative class of initiators capable of initiatingpolymerization of free radically active functional groups in thehardenable resin are those that include free radical-generating thermalinitiators. Examples include peroxides (e.g., benzoyl peroxide andlauryl peroxide) and azo compounds (e.g., 2,2-azobis-isobutyronitrile(AIBN)).

Photoinitiator compounds are preferably provided in dental compositionsdisclosed in the present application in an amount effective to initiateor enhance the rate of cure or hardening of the resin system. Usefulphotopolymerizable compositions are prepared by simply admixing, undersafe light conditions, the components as described above. Suitable inertsolvents may be used, if desired, when preparing this mixture. Anysolvent that does not react appreciably with the components of theinventive compositions may be used. Examples of suitable solventsinclude, for example, acetone, dichloromethane, and acetonitrile.

Polyacid

Compositions of the present invention include at least one polyacid,which may be a non-curable or non-polymerizable polyacid, or a curableor polymerizable polyacid (e.g., a resin-modified polyacid). Typically,the polyacid is a polymer having a plurality of acidic repeating unitsand a plurality of polymerizable groups. In alternative embodiments, thepolyacid may be substantially free of polymerizable groups. The polyacidneeds not be entirely water soluble, but it should be at leastsufficiently water-miscible so that it does not undergo substantialsedimentation when combined with other aqueous components. Suitablepolyacids are listed in U.S. Pat. No. 4,209,434 (Wilson et al.), column2, line 62, to column 3, line 6. The polyacid should have a molecularweight sufficient to provide good storage, handling, and mixingproperties. A typical weight average molecular weight is 5,000 to100,000, evaluated against a polystyrene standard using gel permeationchromatography.

In one embodiment, the polyacid is a curable or polymerizable resin.That is, it contains at least one ethylenically unsaturated group.Suitable ethylenically unsaturated polyacids are described in U.S. Pat.No. 4,872,936 (Engelbrecht), e.g., at columns 3 and 4, and EP 323 120 B1(Mitra), e.g., at page 3, line 55 to page 5, line 8. Typically, thenumbers of acidic groups and ethylenically unsaturated groups areadjusted to provide an appropriate balance of properties in the dentalcomposition. Polyacids in which 10% to 70% of the acidic groups havebeen replaced with ethylenically unsaturated groups are preferred.

In other embodiments, the polyacid is hardenable in the presence of, forexample, an acid-reactive filler and water, but does not containethylenically unsaturated groups. That is, it is an oligomer or polymerof an unsaturated acid. Typically, the unsaturated acid is an oxyacid(i.e., an oxygen containing acid) of carbon, sulfur, phosphorous, orboron. More typically, it is an oxyacid of carbon. Such polyacidsinclude, for example, polyalkenoic acids such as homopolymers andcopolymers of unsaturated mono-, di-, or tricarboxylic acids.Polyalkenoic acids can be prepared by the homopolymerization andcopolymerization of unsaturated aliphatic carboxylic acids, e.g.,acrylic acid, 2-choloracrylic acid, 3-choloracrylic acid, 2-bromoacrylicacid, 3-bromoacrylic acid, methacrylic acid, itaconic acid, maleic acid,glutaconic acid, aconitic acid, citraconic acid, mesaconic acid, fumaricacid, and tiglic acid. Suitable monomers that can be copolymerized withthe unsaturated aliphatic carboxylic acids include, for example,unsaturated aliphatic compounds such as acrylamide, acrylonitrile, vinylchloride, allyl chloride, vinyl acetate, and 2-hydroxyethylmethacrylate. Ter- and higher polymers may be used if desired.Particularly preferred are the homopolymers and copolymers of acrylicacid. The polyalkenoic acid should be substantially free ofunpolymerized monomers.

The amount of polyacid should be sufficient to react with theacid-reactive filler and to provide an ionomer composition withdesirable hardening properties. Typically, the polyacid represents atleast 1 wt-%, more typically at least 3 wt-%, and most typically atleast 5 wt-%, based on the total weight of the unfilled composition.Typically, the polyacid represents at most 90 wt-%, more typically atmost 60 wt-%, and most typically at most 30 wt-%, based on the totalweight of the unfilled composition.

Acid-Reactive Fillers

Suitable acid-reactive fillers include metal oxides, glasses, and metalsalts. Typical metal oxides include barium oxide, calcium oxide,magnesium oxide, and zinc oxide. Typical glasses include borate glasses,phosphate glasses, and fluoroaluminosilicate (“FAS”) glasses. FASglasses are particularly preferred. The FAS glass typically containssufficient elutable cations so that a hardened dental composition willform when the glass is mixed with the components of the hardenablecomposition. The glass also typically contains sufficient elutablefluoride ions so that the hardened composition will have cariostaticproperties. The glass can be made from a melt containing fluoride,alumina, and other glass-forming ingredients using techniques familiarto those skilled in the FAS glassmaking art. The FAS glass typically isin the form of particles that are sufficiently finely divided so thatthey can conveniently be mixed with the other cement components and willperform well when the resulting mixture is used in the mouth.

Generally, the average particle size (typically, diameter) for the FASglass is no greater than about 12 micrometers, typically no greater than10 micrometers, and more typically no greater than 5 micrometers asmeasured using, for example, a sedimentation analyzer. Suitable FASglasses will be familiar to those skilled in the art, and are availablefrom a wide variety of commercial sources, and many are found incurrently available glass ionomer cements such as those commerciallyavailable under the trade designations VITREMER, VITREBOND, RELY XLUTING CEMENT, RELY X LUTING PLUS CEMENT, PHOTAC-FIL QUICK, KETAC-MOLAR,and KETAC-FIL PLUS (3M ESPE Dental Products, St. Paul, Minn.), FUJI IILC and FUJI IX (G-C Dental Industrial Corp., Tokyo, Japan) and CHEMFILSuperior (Dentsply International, York, Pa.). Mixtures of fillers can beused if desired.

The FAS glass can optionally be subjected to a surface treatment.Suitable surface treatments include, but are not limited to, acidwashing (e.g., treatment with a phosphoric acid), treatment with aphosphate, treatment with a chelating agent such as tartaric acid, andtreatment with a silane or an acidic or basic silanol solution.Desirably the pH of the treating solution or the treated glass isadjusted to neutral or near-neutral, as this can increase storagestability of the hardenable composition.

In another embodiment, the acid-reactive filler comprises a non-fusedoxyfluoride material. The oxyfluoride material may include a trivalentmetal, oxygen, fluorine, and an alkaline earth metal. Preferably thetrivalent metal is aluminum, lanthanum, or combinations thereof. Morepreferably the trivalent metal is aluminum. Preferably the alkalineearth metal is strontium, calcium, barium, or combinations thereof. Insome embodiments of the present invention, the oxyfluoride material mayfurther include silicon and/or heavy metal (e.g., zirconium, lanthanum,niobium, yttrium, or tantalum), or more specifically, oxides, fluoridesand/or oxyfluorides thereof.

In some embodiments of the present invention, at least a portion of theoxyfluoride material is nanostructured. Such nanostructured materialsinclude the oxyfluoride material in the form of, for example,nanoparticles, coatings on particles, coatings on aggregates ofparticles, infiltrate in a porous structure, and combinations thereof.Preferably at least 90% by weight, more preferably at least 95% byweight, and most preferably at least 98% by weight of the oxyfluoridematerial is nanostructured.

A description of suitable oxyfluoride materials and their use in dentalcompositions is provided in U.S. patent application Ser. No. 10/847,805,filed on May 17, 2004, now U.S. Pat. No. 7,090,722.

The amount of acid-reactive filler should be sufficient to provide anionomer composition having desirable mixing and handling propertiesbefore hardening and good physical and optical properties afterhardening. Generally, the reactive filler represents less than about 85%of the total weight of the composition. Typically, the acid-reactivefiller represents at least 10 wt-%, and more typically at least 20 wt-%,based on the total weight of the composition. Typically, theacid-reactive filler represents at most 75 wt-%, and more typically atmost 50 wt-%, based on the total weight of the composition.

Nanofillers

The composition of the invention contains one or more nanofillers whichmay be either acid reactive or non-acid reactive. Such nanofillerstypically have an average particle size of at most 200 nanometers andmore typically at most 100 nanometers. Such nanofillers typically havean average particle size of at least 2 nanometers and more typically atleast 5 nanometers. Typically, the nanofiller comprises nanoparticlesselected from silica; zirconia; oxides of titanium, aluminum, cerium,tin, yttrium, strontium, barium, lanthanum, zinc, ytterbium, bismuth,iron, and antimony; and combinations thereof. More typically, thenanofiller comprises nanoparticles selected from silica; zirconia;oxides of titanium; and combinations thereof. In some embodiments, thenanofiller is in the form of nanoclusters, typically at least 80 percentby weight nanoclusters. More typically the nanoclusters include silicaclusters, silica-zirconia clusters, and combinations thereof. In otherembodiments, the nanofiller is in the form of a combination ofnanoparticles and nanoclusters. Often a portion of the surface of thenanofiller is silane treated or otherwise chemically treated to provideone or more desired physical properties.

Suitable nanofillers are disclosed in U.S. Pat. No. 6,387,981 (Zhang etal.) and U.S. Pat. No. 6,572,693 (Wu et al.) as well as InternationalPublication Nos. WO 01/30305 (Zhang et al.), WO 01/30306 (Windisch etal.), WO 01/30307 (Zhang et al.), and WO 03/063804 (Wu et al.). Fillercomponents described in these references include nanosized silicaparticles, nanosized metal oxide particles, and combinations thereof.Nanofillers are also described in U.S. patent application Ser. No.10/847,782, filed on May 17, 2004, now U.S. Patent Publication No.2005/0256223, and U.S. patent application Ser. No. 10/847803, filed onMay 17, 2004, now U.S. Pat. No. 7,090,721.

Typically, the nanofillers of the present invention are non-pyrogenicfillers, however pyrogenic fillers can be added as optional additives tothe dental compositions.

The acid-reactive, non-fused oxyfluoride materials described above thatare at least partially nanostructured can be used as nanofillers in thepresent invention.

The amount of nanofiller should be sufficient to provide an ionomercomposition having desirable mixing and handling properties beforehardening and good physical and optical properties after hardening.Typically, the nanofiller represents at least 0.1 wt-%, more typicallyat least 10 wt-%, and most typically at least 20 wt-% or at least 15wt-%, based on the total weight of the composition. Typically, thenanofiller represents at most 80 wt-%, more typically at most 70 wt-%,and most typically at most 60 wt-%, based on the total weight of thecomposition.

Other Fillers

In addition to the acid-reactive filler and the nanofiller components,the compositions of the present invention can also optionally includeone or more other fillers. Such fillers may be selected from one or moreof a wide variety of materials suitable for the use in dental and/ororthodontic compositions.

The other filler can be an inorganic material. It can also be acrosslinked organic material that is insoluble in the resin component ofthe composition, and is optionally filled with inorganic filler. Thefiller should in any event be nontoxic and suitable for use in themouth. The filler can be radiopaque or radiolucent. The filler typicallyis substantially insoluble in water.

Examples of suitable inorganic fillers are naturally occurring orsynthetic materials including, but not limited to: quartz; nitrides(e.g., silicon nitride); glasses derived from, for example, Zr, Sr, Ce,Sb, Sn, Ba, Zn, and Al; feldspar; borosilicate glass; kaolin; talc;titania; low Mohs hardness fillers such as those described in U.S. Pat.No. 4,695,251 (Randklev); and silica particles (e.g., submicronpyrogenic silicas such as those available under the trade designationsAEROSIL, including “OX 50,” “130,” “150” and “200” silicas from DegussaAG, Hanau, Germany and CAB-O-SIL M5 silica from Cabot Corp., Tuscola,Ill.). Examples of suitable organic filler particles include filled orunfilled pulverized polycarbonates, polyepoxides, and the like.

Suitable non-acid-reactive filler particles are quartz, submicronsilica, and non-vitreous microparticles of the type described in U.S.Pat. No. 4,503,169 (Randklev). Mixtures of these non-acid-reactivefillers are also contemplated, as well as combination fillers made fromorganic and inorganic materials.

The surface of the filler particles can also be treated with a couplingagent in order to enhance the bond between the filler and the resin. Theuse of suitable coupling agents includegamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like. Examples of useful silane coupling agents are thoseavailable from Crompton Corporation, Naugatuck, Conn., as SILQUEST A-174and SILQUEST A-1230.

For some embodiments of the present invention that include other fillers(e.g., dental restorative compositions), the compositions may include atleast 1% by weight, more preferably at least 2% by weight, and mostpreferably at least 5% by weight other filler, based on the total weightof the composition. For such embodiments, compositions of the presentinvention preferably include at most 40% by weight, more preferably atmost 20% by weight, and most preferably at most 15% by weight otherfiller, based on the total weight of the composition.

Water

The compositions of the invention contain water. The water can bedistilled, deionized, or plain tap water. Typically, deionized water isused.

The amount of water should be sufficient to provide adequate handlingand mixing properties and to permit the transport of ions, particularlyin the filler-acid reaction. Preferably, water represents at least 2wt-%, and more preferably at least 5 wt-%, of the total weight ofingredients used to form the composition. Preferably, water representsno greater than 90 wt-%, and more preferably no greater than 80 wt-%, ofthe total weight of ingredients used to form the composition.

Optional Additives

Optionally, the hardenable compositions may contain other solvents,cosolvents (e.g., alcohols) or diluents. If desired, the hardenablecomposition of the invention can contain additives such as indicators,dyes, pigments, inhibitors, accelerators, viscosity modifiers, wettingagents, tartaric acid, chelating agents, surfactants, buffering agents,stabilizers, and other similar ingredients that will be apparent tothose skilled in the art. Additionally, medicaments or other therapeuticsubstances can be optionally added to the dental compositions. Examplesinclude, but are not limited to, fluoride sources, whitening agents,anticaries agents (e.g., xylitol), remineralizing agents (e.g., calciumphosphate compounds), enzymes, breath fresheners, anesthetics, clottingagents, acid neutralizers, chemotherapeutic agents, immune responsemodifiers, thixotropes, polyols, anti-inflammatory agents, antimicrobialagents, antifungal agents, agents for treating xerostomia,desensitizers, and the like, of the type often used in dentalcompositions. Combination of any of the above additives may also beemployed. The selection and amount of any one such additive can beselected by one of skill in the art to accomplish the desired resultwithout undue experimentation.

Preparation and Use of the Compositions

The hardenable dental compositions of the present invention can beprepared by combining all the various components using conventionalmixing techniques. As discussed above, the compositions may be partiallyor fully hardened by an ionic reaction between an acid-reactive fillerand a polyacid. Optionally, the compositions may contain a polymerizablecomponent and a photoinitiator and be hardened by photoinitiation, ormay be partially or fully hardened by chemical polymerization such as aredox cure system in which the composition contains a free-radicalinitiator system, e.g., including an oxidizing agent and a reducingagent. Alternatively, the hardenable composition may contain differentinitiator systems, such that the composition can be both aphotopolymerizable and a chemically polymerizable composition, as wellas an ionically hardenable composition.

The hardenable compositions of the invention can be supplied in avariety of forms including one-part systems and multi-part systems,e.g., two-part powder/liquid, paste/liquid, paste/powder and paste/pastesystems. Other forms employing multi-part combinations (i.e.,combinations of two or more parts), each of which is in the form of apowder, liquid, gel, or paste are also possible. The various componentsof the composition may be divided up into separate parts in whatevermanner is desired; however, the polyacid, acid-reactive filler and watergenerally would not all be present in the same part, although any two ofthese may be grouped together in the same part along with anycombination of other components. Furthermore, in a redox multi-partsystem, one part typically contains the oxidizing agent and another parttypically contains the reducing agent. However, the reducing agent andoxidizing agent could be combined in the same part of the system if thecomponents are kept separated, for example, through use ofmicroencapsulation.

In one embodiment, the composition of the present invention is providedas a two-part, paste-paste system. The first part, Paste A, typicallycontains water, reducing agent, light cure catalyst, FAS glass,non-acid-reactive nanofillers, and radiopacifying nanofillers. Optionalingredients such as reactive nanofillers, nanocluster fillers andcompatible reactive diluents and resins may be added to Paste A. Thesecond part, Paste B, typically contains a polycarboxylic acid modifiedto have a small number of pendant methacrylate groups (See, e.g., U.S.Pat. Nos. 4,872,936, and 5,130,347). Paste B may also contain an acidicmonomer component, nonreactive nanofillers and/or nanocluster fillers,an oxidizing agent, and a light cure catalyst. Optional ingredients forPaste A and Paste B include multifunctional methacrylate resinadditives, stabilizers and colorants. This combination of ingredients inPaste A and Paste B generally provides a stable RMGI composition withprimeness adhesion to dentin and enamel, radiopacity for x-raydiagnosis, and improved aesthetics. Such compositions are especiallyuseful for bulk filling of tooth restorations by a convenient, one-step,easy mix direct restoration method.

In some embodiments, two-part dental compositions of the presentinvention can be provided in a dual barrel syringe having a first barreland a second barrel, wherein the part A resides in the first barrel andthe part B resides in the second barrel. In other embodiments, two-partdental compositions of the present invention can be provided in aunit-dose capsule. In some embodiments, each part of a multi-part dentalsystem can be mixed together using a static mixer.

The components of the hardenable composition can be included in a kit,where the contents of the composition are packaged to allow for storageof the components until they are needed.

When used as a dental composition, the components of the hardenablecompositions can be mixed and clinically applied using conventionaltechniques. A curing light is generally required for the initiation ofphotopolymerizable compositions. The compositions can be in the form ofcomposites or restoratives that adhere very well to dentin and/orenamel. Optionally, a primer layer can be used on the tooth tissue onwhich the hardenable composition is used. The compositions, e.g.,containing a FAS glass or other fluoride-releasing material, can alsoprovide very good long-term fluoride release. Some embodiments of theinvention may provide glass ionomer cements or adhesives that can becured in bulk without the application of light or other external curingenergy, do not require a pre-treatment, have improved physicalproperties including improved flexural strength, and have high fluoriderelease for cariostatic effect.

The hardenable dental compositions of the invention are particularlywell adapted for use in the form of a wide variety of dental materials.They can be used in prosthodontic cements, which are typically filledcompositions (preferably containing greater than about 25 wt-% fillerand up to about 60 wt-% filler). They can also be used in restoratives,which include composites which are typically filled compositions(preferably containing greater than about 10 wt-% filler and up to about85 wt-% filler) that are polymerized after being disposed adjacent to atooth, such as filling materials. They can also be used in prosthesesthat are shaped and hardened for final use (e.g., as a crown, bridge,veneer, inlay, onlay, or the like), before being disposed adjacent to atooth. Such preformed articles can be ground or otherwise formed into acustom-fitted shape by the dentist or other user. Although thehardenable dental composition can be any of a wide variety of materialspreferably, the composition is not a surface pre-treatment material(e.g., etchant, primer, bonding agent). Rather, preferably, thehardenable dental composition is a restorative (e.g., composite, fillingmaterial or prosthesis), cement, sealant, coating, or orthodonticadhesive.

Features and advantages of this invention are further illustrated by thefollowing examples, which are in no way intended to be limiting thereof.The particular materials and amounts thereof recited in these examples,as well as other conditions and details, should not be construed tounduly limit this invention. Unless otherwise indicated, all parts andpercentages are on a weight basis, all water is deionized water, and allmolecular weights are weight average molecular weight.

EXAMPLES Test Methods

Particle Size Determination Test Methods

Average Particle Size by Particle Size Analyzer: Particle size(including cluster size) distribution (based on volume percent) wasdetermined using a Coulter LS 230 Particle Size Analyzer (CoulterCorporation, Hialeah, Fla.). The Analyzer was equipped with aPolarization Intensity Differential Scanning (PIDS) software. A 300-mgsample of filler was added into a glass vial with enough MICRO-90surfactant (Cole-Parmer, Vernon Hills, N.Y.) to wet all the filler. A30-ml aliquot of Calgon Solution (made by thoroughly mixing 0.20 gsodium fluoride, 4.00 g sodium pyrophosphate, 40.00 g sodiumhexametaphosphate, 8.00 g MICRO-90 surfactant, and 3948 ml of DI water)was added and the resulting mixture shaken for 15 minutes and sonicatedby a probe sonicator (Model W-225 Sonicator, Heat Systems-Ultrasonics,Farmingdale, N.Y.) for 6 min at an output control knob setting of 9.Particle analysis was conducted using Coulter LS 230 ParticleCharacterization Software Version 3.01. Testing conditions were 90seconds for Run Length, 0 seconds for Wait Length, and the test samplewas added dropwise into the sample orifice until the PIDS reading wasbetween 45% and 55%. Three sets of data per sample were averaged toobtain the average particle size.

Average Particle Size by TEM (Transmission Electron Microscopy): Samplesapproximately 80-nm thick were placed on 200-mesh copper grids withcarbon stabilized formvar substrates (SPI Supplies, a division ofStructure Probe, Inc., West Chester, Pa.). A transmission electronmicrograph (TEM) was taken using a JEOL 200CX Instrument (JEOL, Ltd. ofAkishima, Japan and sold by JEOL USA, Inc.) at 200 Kv. A population sizeof about 50-100 particles was measured and an average particle size wasdetermined.

Adhesion to Dentin Test Method

Dentin Adhesion (DA): Dentin adhesion was measured according to theprocedure described in U.S. Pat. No. 5,154,762 (Mitra et al.), butwithout using any pretreatment of the dentin and using a light cureexposure time of 20 seconds. Additionally, the sample was conditioned ina humidity chamber at 37° C. and 90% relative humidity for 20 minutesand then stored in deionized water for 24 hours at 37° C.

Adhesion to Enamel Test Method

Enamel Adhesion (EA): Enamel adhesion was measured according to theprocedure described in U.S. Pat. No. 5,154,762 (Mitra et al.), but withthe same cure time and conditioning sequence as described above forDentin Adhesion.

Compressive Strength (CS) Test Method

Compressive strength was evaluated by first injecting a mixedpaste-paste test sample into a glass tube having a 4-mm inner diameter.The ends of the glass tube were plugged with silicone plugs. The filledtubes were subjected to 0.275 megapascal (MPa) pressure for 5 minutes,irradiated with a XL 1500 curing light (3M Company) for 60 seconds, andplaced in a KULZER UniXS (Kulzer, Inc., Germany) light box for 90seconds. Five such cured samples were cut to a length of 8 mm and placedin 37° C. water for 1 day. Compressive strength was determined accordingto ISO Standard 7489 using an INSTRON universal tester (Instron Corp.,Canton, Mass.) operated at a crosshead speed of 1 millimeter per minute(mm/min). Results were reported as the average of 5 replicates.

Diametral Tensile Strength (DTS) Test Method

Diametral tensile strength was measured using the above-described CSprocedure, but using samples were cut to a length of 2 mm. Results werereported as the average of 7 replicates.

Fluoride Release (FR) Test Method

Fluoride release was evaluated in vitro by preparing mixed paste-pastetest samples and placing them in a 20-mm diameter×1-mm high cylindricalmold capped with two plastic sheets clamped under moderate pressureusing a C-clamp. The samples were light cured with a XL 1500 curinglight (3M Company) for 60 seconds from each side, and then stored in ahumidity chamber at 37° C. and 90% relative humidity for one hour. Thesamples were removed from the chamber and each sample immersedseparately in a specimen vial containing 25 ml of deionized water in a37° C. oven for varying periods of time. At each measurement interval, aspecimen vial was removed from the oven and 10 ml of the water wasmeasured out from the specimen vial and combined with 10 ml of TISAB IITotal Ionic Strength Adjustment Buffer (Sigma Aldrich). The resultingsolution was stirred and measured using a fluoride ion selectiveelectrode to determine the cumulative micrograms of fluoride leached pergram of the test sample for the applicable measurement period, using anaverage of three samples. The specimen vials were replenished with freshdeionized water and returned to the oven until the next measurementperiod.

Visual Opacity (MacBeth Values) Test Method

Disc-shaped (1-mm thick×15-mm diameter) paste samples were cured byexposing them to illumination from a VISILUX 2 curing light (3M Co, St.Paul, Minn.) for 60 seconds on each side of the disk at a distance of 6mm. Hardened samples were measured for direct light transmission bymeasuring transmission of light through the thickness of the disk usinga MacBeth transmission densitometer Model TD-903 equipped with a visiblelight filter, available from MacBeth (MacBeth, Newburgh, N.Y.). LowerMacBeth Values indicate lower visual opacity and greater translucency ofa material. The reported values are the average of 3 measurements.

Radiopacity Test Method

Disc-shaped (1-mm thick×15-mm diameter) paste test samples were cured byexposing them to illumination from an VISILUX 2 (3M Company) curinglight for 60 seconds on each side of the disk at a distance of 6 mm. Thecured samples were then evaluated for radiopacity as follows.

For radiopacity evaluation, the procedure used followed the ISO-testprocedure 4049 (1988). Specifically, cured composite samples wereexposed to radiation using a Gendex GX-770 dental X-ray (Milwaukee,Wis.) unit for 0.73 seconds at 7 milliamps and 70 kV peak voltage at adistance of about 400 millimeters. An aluminum step wedge was positionedduring exposure next to the cured disk on the X-ray film. The X-raynegative was developed using an Air Techniques Peri-Pro automatic filmprocessor (Hicksville, N.Y.). A Macbeth densitometer was used todetermine the optical density of the sample disk by comparison with theoptical densities of the aluminum step wedge. The reported values ofoptical density (i.e., radiopacity) are the average of 3 measurements.

Polish Retention Test Method

The polish retention of a hardened sample was measured by the followingmethod. Rectangular-shaped, mixed paste-paste samples (20-mm long×9-mmwide×3-mm thick) were cured with a VISILUX 2 unit (3M Company) for 60seconds. The light cured samples were immediately placed in a humiditychamber for 1 hour at 37° C. and 90% relative humidity. The samples werethen placed in deionized water in an oven at 37° C. for 24 hours. Thesamples were mounted with double-sided adhesive tape (Scotch Brand Tape,Core series 2-1300, St. Paul, Minn.) to a holder and were polishedaccording to the following series of steps that were performedsequentially as shown in Table 1. A Buehler ECOMET 4 Polisher with anAUTOMET 2 Polishing Head was used with clockwise rotation.

TABLE 1 Polishing Sequence of Steps Load (kg) (Abrasive- per Time StepProcedure Grit) Lubricant RPM Sample (Seconds) 1 Polish SiC-320 Water150 1.8 15 2 Rinse Water 3 Polish SiC-600 Water 150 1.8 60 4 Rinse Water5 Master Master Water 120 1.8 60 Polish Polish Abrasive 6 Rinse Water

A micro-tri-gloss instrument (BYK Gardner, Columbia, Md.) was used tocollect photoelectric measurements of specularly reflected light fromthe sample surface after polishing and after toothbrushing. Theprocedure described in ASTM D 523-89 (Reapproved 1994) Standard TestMethod for Specular Gloss, for measurements made at 60° geometry wasfollowed with the following modification. Initial gloss after polishing(G_(I)) was measured for initial sample. (The initial gloss value afterpolishing at 60° geometry was typically 80 to 86.) Final gloss after2000 toothbrushing cycles (G_(F)) was measured. Randomly selected areason the rectangular sample were measured for initial and final gloss.Each sample was brushed for a total of 2000 cycles with an ORAL B 40medium Straight toothbrush (Oral B Laboratories, Belmont, Calif.) usingCREST Regular Flavor (Proctor & Gamble, Cincinnati, Ohio) toothpaste.One operator brushed all of the samples using forces on the order oftoothbrushing forces. Each sample was brushed with the same toothbrush.One toothbrushing cycle was a forward and a back stroke. Percent polishretention was reported as (G_(F))×100/(G_(I)) and was the average of 3replications.

Three-Body Wear Test Method

The wear rate of a cured paste-paste test sample was determined by anin-vitro 3-body wear test using a Davidson Wear Tester Model 2 (ACTA,Amsterdam) unit. The Davidson Wear Tester was calibrated to ensure thatthe wear track was perpendicular to the wheel face. Uncured mixedpaste-paste samples (constituting the first body) were loaded into a10-mm by 4-mm slot on a 47.75-mm diameter wear wheel of the DavidsonWear Tester. The samples were cured for 60 seconds using a VISILUX 2Curing Light (3M Company). The wear wheel, with the cured samplesmounted, measured 50.80 to 53.34 mm in diameter. The cured samples onthe wear wheel were machined smooth using a Carter Diamond Tool device(S-2192 SYN, Carter Diamond Tool Corp., Willoughby, Ohio) turning at 900rpm. Water was flooded onto the wheel to control dust and to dissipateheat during the machining process. The wear wheel was kept as wet aspossible during the machining.

The finial diameter of the first body wear wheel was 48.26 mm±0.254 to0.381 mm. During testing, the first body was allowed to contact anotherwheel (constituting the second body) that acted as an antagonistic cusp.During contact, the two wheels were immersed in a slurry (constitutingthe third body) having 150 grams of ground and filtered bird seed (WildBird Mix, Greif Bros. Corporation, Rosemount, Minn.), 25 grams ofpoly(methyl methacrylate) (QuickMOUNT Powder Ingredient, FultonMetallurgical Products Corp., Valencia, Pa.), and 275 ml of water. Thetwo wheels were counter-rotated against each other for 166,000 cycles.Dimensional loss during these cycles was measured every 39,000 cycles bya Perthometer PRK profilometer (Feinpruef Corp., Charlotte, N.C.) alongthe 10-mm face of the cured and machined composite. Data were collectedin a Wear Version 3 software (ACTA, Amsterdam). The data were plottedusing linear regression and the wear rates for the samples weredetermined by calculating the slope of the lines. The wear rate for eachsample was reported as a change in unit length per number of cycles(e.g., mm/cycle) and then normalized to the wear rate of a standardmaterial, which was selected to be Z250 composite (3M Company). Thus,the reported wear resistance (average of three replications) is adimensionless value.

Abbreviations, Descriptions, and Sources of Materials AbbreviationDescription and Source of Material HEMA 2-Hydroxyethyl methacrylate(Sigma-Aldrich, St. Louis, MO) BisGMA2,2-Bis[4-(2-hydroxy-3-methacryloyloxy-propoxy)phenyl]propane; CAS No.1565-94-2 PEGDMA-400 Polyethyleneglycol dimethacrylate (Sartomer 603; MWabout 570; Sartomer, Exton, PA) AA:ITA Copolymer made from a 4:1 moleratio of acrylic acid:itaconic acid, prepared according to Example 3 ofU.S. Pat. No. 5,130,347 (Mitra), MW (average) = 106,000; polydispersityρ = 4.64. IEM 2-Isocyanatoethyl methacrylate (Sigma-Aldrich) VBCPPolymer made by reacting AA:ITA copolymer with sufficient IEM to convert16 mole percent of the acid groups of the copolymer to pendentmethacrylate groups, according to the dry polymer preparation of Example11 of U.S. Pat. No. 5,130,347. GDMA Glycerol dimethacrylate (Rohm Tech,Inc., Malden, MA) Kayamer PM-2 Bis(methacryloxyethyl) phosphate (NipponKayaku, Japan) Ebecryl 1830 Polyester hexaacrylate resin (UCB-RadCureSpecialties, Brussels, Belgium) DMAPE 4-Dimethylaminophenethanol(Sigma-Aldrich) EDMAB Ethyl 4-(N,N-dimethylamino)benzoate(Sigma-Aldrich) BHT Butylated hydroxytoluene (Sigma-Aldrich) DPIPF6Diphenyliodonium hexafluorophosphate (Johnson Matthey, Alpha AesarDivision, Ward Hill, NJ) CPQ Camphorquinone (Sigma-Aldrich) ATUAllylthiourea (Sigma-Aldrich) KPS Potassium persulfate (Sigma-Aldrich)KH₂PO₄ Potassium dihydrogen phosphate (EM Science, Gibbstown, NJ) K₂SO₄Potassium sulfate (J. T. Baker, Phillipsburg, NJ) MEEAA2-[2-(2-methoxyethoxy)ethoxy]acetic acid (Sigma-Aldrich) Zirconia SolAqueous zirconia sol containing 23% solids prepared as described in U.S.Pat. No. 5,037,579 (Matchette). - Primary average particle size wasdetermined to be 5 nm based on the Crystallite Particle Size and CrystalForm Content Test Method described in U.S. Pat. No. 6,387,981 (Zhang etal.), and average aggregated particle size was determined to be 50-60 nmbased on the Photon Correlation Spectroscopy Test Method described inU.S. Pat. No. 6,387,981 (Zhang et al.) Zirconia Powder Zirconia powder,Buhler Z-W4, (Buhler LTD, Uzwil, Switzerland). Average particle size wasreported by the manufacturer to be 10 nm to 40 nm. SILQUEST A-174γ-Methacryloxypropyltrimethoxysilane used for silane treatment offillers (Crompton Corporation, Naugatuck, CT) SILQUEST A-1230 PEG Silaneused for silane treatment of fillers (Crompton Corporation) AEROSILR812S Fumed silica filler (Degussa, Germany) Filler A (FAS Glass) SchottGlass (Product No. G 018-117; average particle size 1.0 micrometers;Schott Electronic Packaging, GmbH, Landshut, Germany). The filler wassilane-treated as described for Filler FAS VI in U.S. Pat. PublicationNo. 2003/0166740 (Mitra et al.). Filler B (FAS Glass) “Control Glass” asdescribed in Example 1 of U.S. Pat. No. 5,154,762 (Mitra et al.) andsubsequently silane-treated as described for Filler FAS I in U.S. Pat.Publication No. 2003/0166740 (Mitra et al.). Average particle sizeestimated to be 3.0 micrometers, based on the Average Particle Size byParticle Size Analyzer Test Method described herein. Filler C (FASGlass) Same as Filler B, except with additional wet milling to anaverage particle size estimated to be 1.0 micrometers, based on theAverage Particle Size by Particle Size Analyzer Test Method describedherein. Filler D (FAS Glass) A bimodal FAS filler blend of Filler B (50weight %) and Filler C (50 weight %). Filler E (Nanofiller)Silane-treated, non-aggregated, nano-sized silica particles in the formof a dry powder were prepared according to the procedure for Filler A inU.S. Pat. Publication No. 2003/0181541 (Wu et al.). The nominal particlesize of Filler E was assumed to be the same as in the starting Nalco2329 silica sol, i.e., about 75 nanometers. Filler F (Nanofiller)Silane-treated, non-aggregated, nano-sized silica particles in the formof a dry powder were prepared according to the procedure for Filler A inU.S. Pat. Publication No. 2003/0181541 (Wu et al.), except that Nalco2327 was used in place of Nalco 2329. The nominal particle size ofFiller F was assumed to be the same as in the starting Nalco 2327 silicasol, i.e., about 20 nanometers. Filler G (Nanofiller) Silane-treated,nano-sized silica particles loosely aggregated as silica clusters wereprepared in the form of a free-flowing dry powder according to theprocedure for Example 1A in U.S. Pat. Publication No. 2003/0181541 (Wuet al.). The primary silica particles making up the silica clusters wereassumed to be the same size as in the starting Nalco 2329 silica sol,i.e., having a nominal particle size of about 75 nanometers. Filler H(Nanofiller) Silane-treated, nano-sized silica and zirconia particlesloosely aggregated as substantially amorphous clusters were prepared inthe form of a dry powder according to the procedure for Filler B in U.S.Pat. Publication No. 2003/0181541 (Wu et al.). The primary silicaparticles making up the silica/zirconia clusters were assumed to be thesame size as in the starting Nalco 1042 silica sol, i.e., having anominal particle size of about 20 nanometers. Filler I (Prep. Ex. 1A)Silane-treated nano-sized zirconia filler prepared according to(Nanozirconia) Preparatory Example 1A described herein. Filler JRadiopaque zirconia-silica filler prepared as described in U.S. Pat. No.4,503,169 (Randklev). Filler K (Prep Ex. 1B) Silane-treated nano-sizedzirconia filler prepared according to Preparatory Example 1B describedherein.

Starting Materials Preparations Preparatory Example 1A Silane-TreatedNanozirconia

Zirconia Sol (800.0 g; 184 g zirconia) and MEEAA (72.08 g) were chargedto a 1-liter round-bottom flask. The water and acid were removed viarotary evaporation to afford a powder (291.36 g) that was further driedin a forced-air oven (90° C.) to provide a dried powder (282.49 g).Deionized (DI) water (501.0 g.) was added and the powder redispersed.The resulting dispersion was charged to a 2-liter beaker followed by theaddition with stirring of 1-methoxy-2-propanol (783 g; Sigma-Aldrich),SILQUEST A-174 (83.7 g) and SILQUEST A-1230 (56.3 g). The resultingmixture was stirred 30 minutes at room temperature and then separatedinto two quart jars and sealed. The jars were heated to 90° C. for 4.0hours, and the contents concentrated via rotary evaporation to afford aliquid concentrate (621 g).

DI water (2400 g) and concentrated ammonia/water (80.0 g; 29% NH₃) werecharged to a 4-liter beaker followed by the addition over about 5minutes of the liquid concentrate to afford a white precipitate. Theprecipitate was recovered by vacuum filtration and washed with DI water.The resulting wet cake was dispersed in 1-methoxy-2-propanol (661 g) toafford a dispersion that contained 15.33 weight % zirconia. Thesilane-treated zirconia filler was designated Preparatory Example 1A(Filler I).

The above dispersion (1183 g) was combined with Resin A [HEMA (24.06 g)and PEGDMA-400 (39.59 g)] and the water and alcohol removed via rotaryevaporation to afford a translucent paste that contained 80 weight %silane-treated nanozirconia filler.

Preparatory Example 1B Silane-Treated Nanozirconia

Zirconia Powder (50 g) was charged to a quart jar with screw top.Deionized (DI) water (67.2 g) and 1-methoxy-2-propanol (99.5 g) wereadded and the powder dispersed. SILQUEST A-174 (10.23 g) and SILQUESTA-1230 (6.87 g) were added to the resulting dispersion while stirring.The resulting mixture was stirred 10 minutes at room temperature andthen the quart jar was sealed. The jar was heated to 90° C. for 4 hours.

DI water (652 g) and concentrated ammonia/water (21.9 g; 29% NH₃) werecharged to a 2-liter beaker followed by the addition over about 5minutes of the liquid dispersion to afford a white precipitate. Theprecipitate was recovered by vacuum filtration and washed with DI water.The resulting wet cake was placed in a tray and heated to 90° C. for 4hours. The resulting dried filter cake was crushed to afford a drynanozirconia powder that was designated Filler K. The powder could bedirectly dispersed into the liquid ingredient components of the variouscompositions described herein.

Preparatory Example 2 Paste A Compositions

Nine first paste compositions (designated with the letter A as A1through A9) were prepared by combining the ingredients (indicated asparts by weight) as listed in Tables 2A and 2B. Filler I (nanozirconia)was added to the compositions as a paste comprised of 80% nanozirconiain Resin A (HEMA and PEGDMA-400; see Preparatory Example 1A) andreported as a dry-weight basis in the Tables. The Resin A components areincluded as part of the HEMA and PEGDMA-400 components in the Tables.

TABLE 2A Paste A Compositions Components Paste Paste (Parts by Weight)A1 Paste A2 Paste A3 Paste A4 A5 HEMA 6.28 5.50 5.74 7.50 5.91PEGDMA-400 7.72 6.48 6.56 0 7.27 DMAPE 0.42 0.42 0.42 0.42 0.75 CPQ 0.100.10 0.10 0.10 0.05 EDMAB 0 0 0 0 0.10 ATU 0.42 0.42 0.42 0.42 0.75Filler A (FAS) 39.72 40.00 16.39 0 40.00 Filler B (FAS) 0 0 16.39 41.050 Filler D (FAS) 0 0 0 41.05 0 Filler F (Nano) 16.31 19.30 36.05 0 16.28Filler G (Nano) 0 0 8.19 0 0 Filler I (Nano) 20.57 20.44 0 0 20.57AEROSIL R812S 0 0 0 0.49 0 DI Water 8.80 7.45 9.83 9.32 8.33 Total 100100 100 100 100

TABLE 2B Paste A Compositions Components (Parts by Weight) Paste A6Paste A7 Paste A8 Paste A9 HEMA 6.28 6.28 6.28 6.28 PEGDMA-400 7.73 7.737.73 7.73 CPQ 0.05 0.05 0.05 0.05 EDMAB 0.09 0.09 0.09 0.09 Filler A(FAS) 77 38.5 19.3 40.0 Filler F (Nano) 0 38.5 57.7 16.3 Filler K (Nano)0 0 0 20.7 DI Water 8.85 8.85 8.85 8.85 Total 100 100 100 100

Preparatory Example 3 Paste B Compositions

Nine second paste compositions (designated with the letter B as B1through B9) were prepared by combining the ingredients (indicated asparts by weight) as listed in Tables 3A and 3B.

TABLE 3A Paste B Compositions Components (Parts by Weight) Paste B1Paste B2 Paste B3 Paste B4 Paste B5 Paste B6 HEMA 20.15 18.92 18.92 5.0623.88 20.07 VBCP 10.85 10.19 10.19 16.82 10.23 10.85 AA:ITA 0 0 0 6.80 00 Polyacid (80:20 wt.-%) GDMA 4.56 4.28 8.12 0 8.12 4.56 BisGMA 2.742.57 4.88 0 4.88 2.74 Kayamer PM-2 5.17 4.85 5.00 0 0 5.17 Ebecryl 18300.56 0.53 1.00 0 1.00 0.56 BHT 0.0108 0.01 0.01 0 0.01 0.08 DPIPF6 0.200.20 0.20 0.20 0.20 0.15 KPS 0.50 0.50 1.80 1.58 1.80 1.00 Filler E53.50 56.15 50.00 0 50.00 26.53 (Nano) Filler J 0 0 0 60.00 0 0 Filler H0 0 0 0 0 26.53 (Nano) AEROSIL 1.77 1.85 0 0 0 1.77 R812S DI Water 0 0 09.74* 0 0 Total 100 100 100 100 100 100 *Saturated salt solutioncontaining KH₂PO₄ (10.72 wt. %) and K₂SO₄ (3.32 wt. %) in DI water.

TABLE 3B Paste B Compositions Components Paste Paste (Parts by Weight)B7 B8 Paste B9 HEMA 20.26 20.26 20.26 VBCP 10.91 10.91 10.91 GDMA 4.584.58 4.58 BisGMA 2.76 2.76 2.76 Kayamer PM-2 5.20 5.20 5.20 Ebecryl 18300.56 0.56 0.56 BHT 0.08 0.08 0.08 DPIPF6 0.15 0.15 0.15 Filler E (Nano)0 26.90 26.90 Filler J 53.80 26.90 0 Filler H (Nano) 0 0 26.90 AEROSILR812S 1.70 1.70 1.70 Total 100 100 100

Examples 1-9 and Comparative Examples 1-2 Paste A-Paste B Compositions

Hardenable compositions (Examples 1-9 and Comparative Examples 1-2) wereprepared by spatulating a first paste with an equal volume of a secondpaste for 25 seconds. The relative parts by weight of pastes utilizedand the parts by weight components in the compositions are provided inTables 4A and 4B.

The hardenable compositions were evaluated for Compressive Strength(DS), Diametral Strength (DTS), Dentin Adhesion (DA), Enamel Adhesion(EA), Visual Opacity, Radiopacity, Fluoride Release, Polish Retention,and Three-Body Wear according to the Test Methods described herein andthe results are reported in Tables 5A and 5B.

TABLE 4A Paste A + Paste B Compositions Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5Comp. Ex. 1 Paste A1 + Paste Paste A2 + Paste Paste A3 + Paste PasteA3 + Paste Paste A5 + Paste Paste A4 + Paste Components B1 B2 B3 B5 B6B4 (Parts by Weight) (1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.20:1 wt.ratio) (1.20:1 wt. ratio) (1.27:1 wt. ratio) (1.20:1 wt. ratio) HEMA12.39 11.41 11.73 13.98 12.15   6.39 PEGDMA-400 4.32 3.62 3.58 3.58 4.070 VBCP 4.78 4.49 4.63 4.65 4.78   7.64 AA:ITA Polyacid 0 0 0 0 0   3.09(80:20 wt.-%) GDMA 2.01 1.89 3.69 3.69 2.01 0 BisGMA 1.21 1.13 2.22 2.221.21 0 Kayamer PM-2 2.28 2.13 2.27 0 2.28 0 DMAPE 0.23 0.23 0.23 0.230.42   0.23 CPQ 0.06 0.06 0.05 0.05 0.04   0.05 EDMAB 0 0 0 0 0.06 0 ATU0.23 0.23 0.23 0.23 0.42   0.23 Ebecryl 1830 0.25 0.23 0.45 0.45 0.25 0BHT 0.005 0.005 0.005 0.005 0.04 0 DPIPF6 0.09 0.09 0.09 0.09 0.07 0 KPS0.22 0.22 0.82 0.82 0.44   0.72 Filler A (FAS) 22.22 22.38 8.94 8.9422.38 0 Filler B (FAS) 0 0 8.94 8.94 0 0 Filler D (FAS) 0 0 0 0 0  44.89 Filler E (Nano) 23.57 24.74 22.73 22.73 11.69 0 Filler F (Nano)9.12 10.80 19.66 19.66 9.11 0 Filler G (Nano) 0 0 4.47 4.47 0 0 Filler H(Nano) 0 0 0 0 11.69 0 Filler I (Nano) 11.51 11.44 0 0 11.51 0 Filler J0 0 0 0 0   27.27 AEROSIL R812S 0.78 0.81 0 0 0.78   0.27 DI Water 4.924.17 5.36 5.36 5.36   4.66 Total 100 100 100 100 100 100*  *Alsocontains KH₂PO₄ and K₂SO₄ that were present in the Paste B4 component.

TABLE 4B Paste A + Paste B Compositions Comp. Ex. 2 Ex. 6 Ex. 7 Ex. 8Ex. 9 Paste A6 + Paste Paste A7 + Paste Paste A7 + Paste Paste A8 +Paste Paste A9 + Paste Components B7 B8 B7 B8 B9 (Parts by Weight)(1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.27:1 wt.ratio) (1.27:1 wt. ratio) HEMA 12.44 12.44 12.44 12.44 12.44 PEGDMA-4004.32 4.32 4.32 4.32 4.32 VBCP 4.81 4.81 4.81 4.81 4.81 GDMA 2.02 2.022.02 2.02 2.02 BisGMA 1.22 1.22 1.22 1.22 1.22 Kayamer PM-2 2.29 2.292.29 2.29 2.29 CPQ 0.03 0.03 0.03 0.03 0.03 EDMAB 0.05 0.05 0.05 0.050.05 Ebecryl 1830 0.25 0.25 0.25 0.25 0.25 BHT 0.04 0.04 0.04 0.04 0.04DPIPF6 0.07 0.07 0.07 0.07 0.07 Filler A (FAS) 43.08 21.54 21.54 10.8022.38 Filler E (Nano) 0 0 11.85 11.85 11.85 Filler F (Nano) 0 21.5421.54 32.28 9.12 Filler H (Nano) 0 0 0 0 11.85 Filler K (Nano) 0 0 0 011.58 Filler J 23.70 23.70 11.85 11.85 0 AEROSIL R812S 0.78 0.78 0.780.78 0.78 DI Water 4.95 4.17 5.36 5.36 5.36 Total 100 100 100 100 100

TABLE 5A Paste A + Paste B Compositions - Evaluation Results Ex. 1 Ex. 2Ex. 3 Ex. 4 Ex. 5 Comp. Ex. 1 Paste A1 + Paste Paste A2 + Paste PasteA3 + Paste Paste A3 + Paste Paste A5 + Paste Paste A4 + Paste B1 B2 B3B5 B6 B4 Test (1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.20:1 wt. ratio)(1.20:1 wt. ratio) (1.27:1 wt. ratio) (1.20:1 wt. ratio) CompressiveStrength 290 312 272 266 289 211 (MPa) Diametral Tensile 55 59 44 41 5035 Strength (MPa) Dentin Adhesion 6.3 4.0 7.0 6.0 5.2 3.2 (MPa) EnamelAdhesion 7.2 5.0 7.2 3.9 6.9 5.6 (MPa) Visual Opacity 0.30 0.35 0.300.34 0.31 0.53 Radiopacity 1.80 1.74 0.85 0.85 2.11 1.75 FluorideRelease 417 NT* NT NT 380 NT (at 24 hours) (μgF/g sample) PolishRetention 22 33.4 NT NT 30.2 NT (%) Three-Body Wear 4.5 3.02 NT NT NT NT*NT = Not Tested

TABLE 5B Paste A + Paste B Compositions - Evaluation Results Comp. Ex. 2Ex. 6 Ex. 7 Ex. 8 Ex. 9 Paste A6 + Paste Paste A7 + Paste Paste A7 +Paste Paste A8 + Paste Paste A9 + Paste B7 B8 B7 B8 B9 Test (1.27:1 wt.ratio) (1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.27:1 wt. ratio) (1.27:1wt. ratio) Nanofiller Level (wt. %) 0 21.54 33.39 44.13 44.40Compressive Strength (MPa) 263 277 298 311 289 Visual Opacity 0.45 0.430.42 0.27 0.31 Radiopacity 2.30 1.44 0.86 0.45 1.80 Polish Retention (%)7.3 26.8 29.7 40.4 30.2

The results in Table 5B show that as the level of nanofiller in thecompositions increases, the compressive strength and polish retentionimproves. The translucency (Visual Opacity) of the hardened paste-pastecompositions also improves with high levels of nanofiller (e.g.,Examples 8 and 9).

Comparative Example 3 VITREMER Glass Ionomer Restorative

The commercial powder-liquid VITREMER resin modified glass ionomerrestorative product (3M Company) was dispensed and hand-mixed accordingto manufacture's directions and the resulting material was evaluated forCompressive Strength (DS), Diametral Tensile Strength (DTS), DentinAdhesion (DA), Enamel Adhesion (EA), Visual Opacity, Radiopacity,Fluoride Release, Polish Retention, and Three-Body Wear according to theTest Methods described herein and the results are reported in Table 6.

TABLE 6 VITREMER Glass Ionomer Test Restorative Product CompressiveStrength (MPa) 208 Diametral Tensile Strength (MPa) 41 Dentin Adhesion(MPa) 0 Enamel Adhesion (MPa) 2.2 Visual Opacity 0.53 Radiopacity 1.85Fluoride Release 326 (at 24 hours) (μgF/g sample) Polish Retention (%)10.4 (Initial gloss after polish was 60) Three-Body Wear 5.4

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

1. A hardenable dental composition comprising: (a) a polyacid; (b) anacid-reactive filler: (c) at least one non-pyrogenic nanofiller; and (d)water; wherein the composition upon hardening has a visual opacity of nomore than about 0.50.
 2. The composition of claim 1, wherein thecomposition upon hardening has a visual opacity of no more than about0.40.
 3. The composition of claim 1, wherein the composition uponhardening has a visual opacity of no more than about 0.30.
 4. Thecomposition of claim 1, wherein at least one of the nanofillers and theacid-reactive filler are the same compound.
 5. The composition of claim1, wherein the composition comprises at least 15 weight percent thenanofiller or combination thereof.
 6. The composition of claim 1,wherein the composition comprises at least 20 weight percent thenanofiller or combination thereof.
 7. The composition of claim 1,wherein the nanofiller or combination thereof has an average particlesize of at most 100 nanometers.
 8. The composition of claim 1, furthercomprising a polymerizable component.
 9. The composition of claim 8,wherein the polymerizable component comprises an ethylenicallyunsaturated compound.
 10. The composition of claim 9, wherein thepolymerizable component comprises an ethylenically unsaturated compoundwith acid functionality.
 11. The composition of claim 10, wherein theacid functionality includes an oxygen-containing acid of carbon, sulfur,phosphorous, or boron.
 12. The composition of claim 10, wherein thepolyacid and the ethylenically unsaturated compound with acidfunctionality are the same.
 13. The composition of claim 1, wherein thepolyacid comprises a polymer having a plurality of acidic repeatinggroups but is substantially free of polymerizable groups.
 14. Thecomposition of claim 13, further comprising a polymerizable component.15. The composition of claim 1, wherein the polyacid comprises a polymerhaving a plurality of acidic repeating groups and a plurality ofpolymerizable groups.
 16. The composition of claim 15, furthercomprising a polymerizable component.
 17. The composition of claim 1,wherein the composition is substantially free of fumed silica andpyrogenic fillers.
 18. The composition of claim 1, wherein theacid-reactive filler is selected from the group consisting of metaloxides, glasses, metal salts, and combinations thereof.
 19. Thecomposition of claim 18, wherein the acid-reactive filler comprises afluoroaluminosilicate (FAS) glass.
 20. The composition of claim 19,wherein the composition comprises less than 50 weight percent FAS glass.21. The composition of claim 19, wherein the composition comprises lessthan 30 weight percent FAS glass.
 22. The composition of claim 19,wherein the composition comprises less than 20 weight percent FAS glass.23. The composition of claim 1, wherein the acid-reactive fillercomprises an oxyfluoride material.
 24. The composition of claim 23,wherein at least 90% by weight of the oxyfluoride material isnanostructured.
 25. The composition of claim 1, wherein at least one ofthe nanofillers is acid reactive.
 26. The composition of claim 1,wherein at least one of the nanofillers is non-acid reactive.
 27. Thecomposition of claim 1, wherein the nanofiller or combination thereofcomprises particles selected from the group consisting of silica;zirconia; oxides of titanium, aluminum, cerium, tin, yttrium, strontium,barium, lanthanum, zinc, ytterbium, bismuth, iron and antimony, andcombinations thereof.
 28. The composition of claim 1, wherein thenanofiller or combination thereof comprises particles selected from thegroup consisting of silica; zirconia; oxides of titanium; andcombinations thereof.
 29. The composition of claim 1, wherein thenanofiller comprises nanoclusters.
 30. The composition of claim 1,wherein the nanofiller comprises at least 80 weight percentnanoclusters.
 31. The composition of claim 29, wherein the nanoclustersare selected from the group consisting of silica clusters,silica-zirconia clusters, and combinations thereof.
 32. The compositionof claim 29, wherein the nanoclusters contain reactive ions.
 33. Thecomposition of claim 8, further comprising a redox cure system.
 34. Thecomposition of claim 8, further comprising a photoinitiator system. 35.The composition of claim 1, further comprising at least one additiveselected from the group consisting of other fillers, pyrogenic fillers,fluoride sources, whitening agents, anticaries agents, remineralizingagents, enzymes, breath fresheners, anesthetics, clotting agents, acidneutralizers, chemotherapeutic agents, immune response modifiers,medicaments, indicators, dyes, pigments, wetting agents, tartaric acid,chelating agents, surfactants, buffering agents, viscosity modifiers,thixotropes, polyols, antimicrobial agents, anti-flammatory agents,antifungal agents, stabilizers, agents for treating xerostomia,desensitizers, and combinations thereof.
 36. The composition of claim 1,wherein a portion of the surface of the nanofiller is chemicallytreated.
 37. The composition of claim 1, wherein a portion of thesurface of the nanofiller is silane treated.
 38. The composition ofclaim 8, wherein the composition is selected from the group consistingof dental restoratives, dental adhesives, dental cements, cavity liners,orthodontic adhesives, dental sealants, and dental coatings.
 39. Thecomposition of claim 1, wherein the composition comprises a multi-partcomposition comprising a first part and a second part, wherein each partcan independently be selected from the group consisting of a liquid,paste, gel, and powder.
 40. A hardenable dental composition comprising:(a) a polyacid; (b) an acid-reactive filler; (c) at least onenon-pyrogenic nanofiller or combination thereof; and (d) water; whereinthe composition upon hardening has a polish retention of at least 10percent.
 41. The composition of claim 40, wherein the composition uponhardening has a polish retention of at least 20 percent.
 42. Thecomposition of claim 40, wherein the composition upon hardening has apolish retention of at least 30 percent.
 43. A method of preparing adental article said method comprising the steps of: (a) providing adental composition of claim 1, or 40; and (b) hardening the dentalcomposition to form the dental article.
 44. The method of claim 43,wherein the dental article is selected from the group consisting ofdental mill blanks, dental crowns, dental fillings, dental prostheses,and orthodontic devices.